We are studying the modulation of the transcription processes in E. coli, using the gal operon and phage lambda as model systems. We have defined so far the functional behavior of several regulatory elements--cyclic AMP, CRP, Rho, Nus and N--that modulate transcription. We have evidence which suggest that each of these elements modulate gene transcription in more than one of the following ways: Activation of initiation, Inhibition of Initiation, Activation of termination, Inhibition of termination. The molecular mechanisms are currently being investigated. In our continuing effort to characterize the complete regulatory features of the gal operon, we have now identified the in vivo transcription initiation sites of the gal mRNA from the two (p1 and p2) promoters of gal both by sizing the mRNAs and by capping the triphosphate ends with labeled 32P-GTP and then sequencing the labeled RNaseT1 fragments. We have also discovered a locus within the first structural gene that regulates gal transcription.